Identified and Inclusive Charged Hadron
Spectra from PHENIXCarla M Vale
Iowa State Universityfor the PHENIX Collaboration
WWND, March 14 2006
WWND, La Jolla, CA 03/14/06
Carla M. Vale 2
Motivation
Particle distributions in transverse momentum provide the most basic tool to investigate the mechanisms of particle production, transport and hadronization
Low pT High pT
hydro evolution & thermalization
energy loss
jet production
chemical composition (through particle ratios)
fragmentation
recombination
WWND, La Jolla, CA 03/14/06
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Detecting Particles in PHENIX
h+h-
Charged hadron tracking and momentum measurements use Pad Chambers (PC1 - PC3), Drift Chamber (DC)
||<0.35, =
WWND, La Jolla, CA 03/14/06
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Identifying Particles in PHENIX
WWND, La Jolla, CA 03/14/06
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RHIC-supplied data sets
p+p d+Au Au+Au Cu+Cu
200 GeV
130 GeV
62.4 GeV
22.4 GeV
en
erg
y
dep
en
den
ce
system size dependence
reference points
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Charged Hadron Spectra
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h± in Au+Au √sNN = 200GeV
PRC 69,034910 (2004)
Charged hadron spectra measured up to ~ 10 GeV
WWND, La Jolla, CA 03/14/06
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h± in Au+Au √sNN = 62.4GeV
4M events divided in 3 centrality bins
p+p reference: interpolation of data from ISR, UA1 and PHENIX + fit using modified Hagedorn function
WWND, La Jolla, CA 03/14/06
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h± in Cu+Cu √sNN = 200GeV
Collis
ion
cen
tralit
y
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Identified Particle Spectra
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π± in d+Au √sNN = 200GeV
Final results on identified particles in d+Au (and p+p) just released: nucl-ex/0306010
WWND, La Jolla, CA 03/14/06
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K± in d+Au √sNN = 200GeV
WWND, La Jolla, CA 03/14/06
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p, p in d+Au √sNN = 200GeV
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π, K, p in Cu+Cu √sNN = 200GeV
Same shapes as in Au+Au
WWND, La Jolla, CA 03/14/06
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Nuclear Modification Factors
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Initial vs Final State Effects
PHENIX Preliminary
High pT suppression not observed in d+Au collisions, final state effects such as parton energy loss are the favored scenario but the energy loss mechanisms are not yet fully understood.
PRC 69, 034910 (2004)
WWND, La Jolla, CA 03/14/06
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System size and Npart
Mid-central Au+Au very similar to central Cu+Cu, for bins with approximately the same <Npart>
Au+Au
Cu+Cu
<Npart> = 114
<Npart> = 98
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Energy Dependence
Au + Au at 62.GeV:
• Qualitatively similar to the 200GeV result
• Less suppression at intermediate pT
• Charged hadrons not as suppressed as π0
WWND, La Jolla, CA 03/14/06
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h± ≠ π0
At intermediate pT, charged hadrons are less suppressed than π0s; at high pT the difference disappears we should look at identified hadrons
RAA (h+ + h-)/2
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RAuAu for π, K, p √sNN = 200GeV
nucl-ex/0603010
Protons are not suppressed like pions and kaons at intermediate pT in central collisions.
WWND, La Jolla, CA 03/14/06
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RCuCu for π, K, p √sNN = 200GeV
Similarity between Cu+Cu and Au+Au for equivalent Npart also seen for identified particles
WWND, La Jolla, CA 03/14/06
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Baryon Anomaly
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Initial Observation
PRL 91,172301 (2003)
Proton/pion > 1 for central Au+Au at intermediate pT
Much larger than expected from fragmentation alone (measured in e+e-)
Anti-proton/pion not as large
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At lower energy
The ratio p/π+ grows faster with pT than at higher energy, and appears to peak earlier
Anti-p/π- similar at both energies up to pT ~ 2 GeV
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Centrality dependence @ Au+Au √sNN = 62.4GeV
Weaker centrality dependence
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And in smaller systems
p/π+ not as high in central Cu+Cu as in central Au+Au
Npart scaling is seen here as well (pT = 2GeV)
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Baryons and mesons behave differently at RHIC in more ways than one…
p/π ratio, RAA, elliptic flow, all show same pattern at pT > 2GeV
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… and it’s not just due to the mass.
The mass is similar to that of a proton, but in both RAuAu and elliptic flow (?), the behaves like the lighter mesons.
WWND, La Jolla, CA 03/14/06
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Recombination?
Fries, R et al PRC 68 (2003) 044902Greco, V et al PRL 90 (2003) 202302Hwa, R et al PRC 70(2004) 024905
At intermediate pT recombination of partons may be a more efficient mechanism of hadron production than fragmentation
WWND, La Jolla, CA 03/14/06
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SummaryStudying spectra gives us a window into particle production at RHIC:
Study system size and energy dependence
Compare to reference systems
At high pT:
Suppression also seen at lower energy Au+Au and in Cu+Cu
Cu+Cu and Au+Au behave similarly for the same <Npart>
Charged hadrons and π0 appear to converge again at high pT
At intermediate pT :
Baryon enhancement is observed in several measurements
p/π+ reaches higher values at lower energy Au+Au
WWND, La Jolla, CA 03/14/06
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Coming soon…
• More results:– Analyses of Cu+Cu 62.4GeV and
22.5GeV data sets are underway and first results will be out very shortly
• More data:– Reference p+p data sets at 62.4GeV
(and possibly 22.4GeV) will be collected during Run6, allowing for more precision in RAA results at those energies
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backup
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Trend at 62GeV Au+Au described by reco +
fragmentationnucl-th/0412043, Greco, Ko and Vitev
WWND, La Jolla, CA 03/14/06
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p/π in d+Au, Au+Au
d+Au similar to peripheral Au+Au but much smaller than central Au+Au
WWND, La Jolla, CA 03/14/06
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RdAu for π, K, p √sNN = 200GeV
nucl-ex/0603010
Species dependence of Cronin effect seen for pT>1.5GeV
Most peripheral collisions very similar to p+p
Calculation by Accardi & Gyulassy PLB586, 244 (2004)
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RAuAu RdAu for protons
Cronin effect in d+Au larger than Au+Au
No centrality dependence in Au+Au above 1.5 GeV